Telephone system



D. C. CROWE TELEPHONE SYSTEM Dec. 24, 1935.

Filed Aug. 19, 1933 2 Sheets-Sheet'l J Cram/ Dec. 24, 1935. D. c. CROWED 14 TELEPHONE SYSTEM Filed Aug. 19, 1933 2 Sheets-Sheet 2 ii? 5H? 7 3the first mentioned subscriber.

Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE TELEPHONE SYSTEMApplication August 19, 1933, Serial No. 685,944 In Sweden August 29,1932 9 Claims.

The present invention relates to telephone systems. More particularlythe invention relates to telephone systems with party lines in whicheach of the subscribers stations allotted to the party line is providedwith a relay which upon being energized brings about the connection ofthe station to the line. A primary object of the invention is to provideswitching means at the subscribers stations and at the exchange adaptedto ensure that only the subscriber of the party line first calling canconnect his telephone apparatus to the line whereby other subscribersallotted to the line are prevented from overhearing or disturbing aconversation carried on by Another object of the invention is to designthe switching means disposed at the subscribers stations for a minimumof energy consumption. The invention is substantially characterized bythe provision at each one of the subscribers stations of a relayarranged to connect the station to the line and to be energized by meansof discharge current from a condenser disposed at the subscribersstation and adapted to be charged to the necessary voltage by means of acurrent source disposed in the exchange. In systems with central batteryfeed said current source may, for example, consist of the normal feedbattery. In local battery systems having a special current source in theexchange for call marking said latter current source may be used forcharging the condensers. The party line used may consist of a doubleline with or without earth connection at the subscribers stations, or ofa single line with earth return. The invention may find application inautomatic as well as in manual telephone systems.

The invention will now be more closely described with reference to theaccompanying drawings showing a plurality of embodiments of the same.Figure 1 shows a circuit diagram for an automatic exchange to which isconnected a party line with three subscribers stations. Figures 2, 4 and5 show circuit diagrams for subscribers stations. Figure 3 shows acircuit diagram for a party line with two subscribers and equipped withcertain arrangements for signalling. Figure 6 shows a circuit diagramfor a manual exchange provided with equipment for serving a party lineconnected thereto.

In the embodiment shown in Figures 1 and 2 the condenser arranged ateach subscribers station is adapted to be charged from the exchange witha voltage volts) exceeding the normal feed voltage which is assumed tobe 32 volts.

I and 2 designate the two branches of the party line. The condenser 3 ateach subscribers station is connected with one pole to the line branch Iand with its other pole to the switch hook 4 of the subscribers set. Thebell 5 is with 5 one pole connected to the line branch 2 and with itsother pole normally connected to the switch hook 4 through a contact 6of the latter. When the microtelephone is removed from the switch hookthe contact 6 is opened and a relay I is 10 simultaneously shunted tothe condenser 3 through a contact 8 of the switch. The microtelephone 9,I0 is connected to the line branches 5 and 2 via a normally open contactII controlled by the relay I. A relay I2 is connected 15 between theline branches I and 2 by means of a normally open contact I3 controlledby the relay 1 and by means of a normally closed contact IA of theswitch hook. I designates an impulse sender. In the exchange D the linebranch I is connected to the negative pole of a 50 volts battery througha contact I5 controlled by the cut-off relay BR, through the line relayLR, and through the resting contact I6 of said relay and a resistanceI'I connected to the nega- 25 tive pole of a 50 volts battery. The linebranch I is also arranged to be connected through the working contact I8of the line relay LR to a point of the battery having a voltage of 32volts. The line branch 2 is connected to the bank of the searcher S andalso, through the resting contact I9 of the relay BR,tothe positive poleof the battery. The other switching members in the exchange are arrangedin a manner known per se. 35

When the line is free all condensers 3 on the line are charged to avoltage of 50 volts. When a subscriber makes a call the relay "I isshunted to the condenser 3 through the contact 8 of the switch hook. Thedischarging current of the condenser energizes the relay '2! whichoperates and closes the contacts II and I3 and actuates the lockingmember 2I by means of which the armature of the relay is mechanicallylocked in attracted position. The closing of the contact I I completes acircuit to the exchange over the branch 2 of the line through thecontact I9 of the relay BR to the positive pole of the battery, and overthe branch i of the line through contact I5, relay LR, contact I6 andresistance I! to the negative pole of the battery (-50 volts). Relay LRoperates, opening contact I6 and closing contact I8. As a result thevoltage impressed upon the line is reduced from 50 volts to 32 volts.The

relays I disposed at the subscribers stations are dimensioned in such amanner that they operate in response to the discharging current from thecondensers 3 when the latter have been charged with the voltage (in thepresent case volts) impressed upon the line when it is'free but not whenthey have been charged to the voltage (32 volts) impressed upon the lineafter one of the subscribers has made a call (on account of the -voltagedrop in the line the charging voltage of the condensers will in thelatter case'be less than V 32 volts) If thus, after the line has beenengaged one of the other subscribers allotted to the line removes hismicrotelephone the appertaining relay I will not operate and thesubscriber in question can consequently not connect himself to the line.Upon operation of the line relay LR, the starting circuit for thesearcher S is also closed through contact 29 whereby the party line ishunted up and connected to a free selector in a manner known per se.

When the subscriber first calling has completed the conversation andreplaces his microtelephone the relay I2 is connected to the linebranches through contact I4 of the switch hook. The circuit for therelay [2 was prepared in advance upon operation of the relay I throughthe closing of contact [3. The relay i2 is therefore energized (from thefeed battery in the exchange) upon being connected to the line andreleases the locking arrangement 2| for the armature of the relay 1,said armature then returning to its position of rest thereby opening thecontacts H and I3. Contact I l interrupts the talking circuit andcontact I3 interrupts the circuit for the relay I2. The opening ofcontact ll causes deenergization of the current feed relay SR in theexchange whereby in a manner known per se, the circuit for the cut-offrelay BR is interrupted and the connection released.

It is not necessary 'for the application of the invention to impressupon the line when free a voltage (50 volts) exceeding the voltageimpressed upon the line when engaged (32 volts) in order thereby toobtain the necessary difference in charging voltage for the condensers 3when the line is free and engaged respectively as in the embodiment nowdescribed; If the relays 1 are sufliciently sensitive the arrangementwill operate even if the same voltage is impressed upon the line whenfree'andwhen engaged. This is due to the fact that the voltage dropoccurring in the line upon connection thereto of a subscribers stationreduces the charging voltage for the condensers 3 in the othersubscribers stations to a value varyingin accordance with the distancefrom the exchange. Also in the subscribers station nearest to theexchange the charging voltage in question is sufiiciently much lowerthan the charging voltage when the line is free to prevent thedischarging current from the condenser in that subscribers station, fromwhich a. call is made after the line is engaged, to obtain such a valuethat the relay 1 operates.

The release of the armature of the relay 1 may also be effectedmechanically. Figure 1c shows a circuit diagram of such an arrangement.Upon replacing the microtelephone the switch hook 4 actuates the lockingarrangement 2| whereby the armature of. the relay I is released.

In the circuit arrangements shown in Figure 2 the signal bell 5 isshunted over the line in series with a separate condenser 23, whereas,when the switch hook is depressed, the condenser 3 is connected inseries with a resistance which in Figure 2A is shown as an inductiveresistance and in.

current sent out.

Figure 213 as an ohmic resistance. Said circuit arrangements entailcertain advantages in signalling. When effecting signalling withperiodically transmitted alternating current in the circuit arrangementaccording to Figure 1 the bat- 5 tery is connected to the line duringthe intervals between the ringing periods to render possible thecharging of the condenser of the called subscriber so that saidsubscriber will be connected to the line when removing hismicrotelephone. 10 During the ringing periods the charge of the.condenser 3 will vary in time with the alternating current wherefore thesubscriber cannot be sure to be connected to the line if removing hismicrotelephone during such a period. Inthe circuit 15 arrangement shownin Figure 2 the time constant for the condenser 3 with resistance 25must have such a value that the charge of the condenser is notappreciably influenced by the .alternating Provided that. the battery is20 maintained connected to the line during the entire ringing time-thusduring the ringing periods as well as during the intervals between thesame the condenser of the called subscriber will maintain a' constantcharging voltage during the en-Ili tire ringing time and the subscribermay consequently obtain connection at an arbitrary moment i the ringingperiod.

In the circuit arrangements shown in Figures 4 and 5 the relays arearranged to be selected 30 with respect to the direction of thedischarging current from the condenser 3. In the arrangement accordingto Figure 4 the necessary selectivity is obtained by making the relaypolarized and in the arrangement according to Figure 5'by 85 means of arectifier 21 connected in series with the relay L The arrangement in theexchange is then such that the battery provided for charging thecondensers has its poles reversed when the first call is received. Thecondensers 3 in 40 the other subscribers stations thereby obtaincharging potential of opposite sign. Upon a call from another subcriberallotted to the line the discharging current through the relay I of saidlatter subscriber will thus have the opposite di- 5 rection, saiddischarging current being unable, on account of the selectivearrangement, toenergize the relay in question. Thus the subscriber lastcalling cannot connect his set to the line.

Figure 6 shows a circuit diagram for a manual 50 exchange to which isconnected a party line consisting of a single conductor and earthreturn, said exchange being provided with an arrangement causing thepotential connected to the line to change its sign upon the occurrenceof a call. 65 y A battery 23 is connectedwith its positive pole to earthand when the line is free, with its negative pole through a slow actingrelay LE1, the resting contact 31 of the relay LE2 and the restingcontact 33 of the relay BR to the line. Upon a call the relay LE1operates and closes its contact 32 whereby a circuit is closed fromearth to a slow acting relay LE2 and a battery 29 the negative pole ofwhich is earthed. The relay LE2 operates and interrupts at contact 3!the circuit for the relay LE1 and connects through contact 3i! thepositive pole of the battery 29 to the line.

Figure 3 shows a circuit diagram for a party line having only twosubscriber, the bell of one subscriber being connected between one ofthe line branches and earth and the bell of the other subscriber betweenthe other branchand earth, and in which selective ringing is arrangedThe bell 40 of the subscriber A is connected between 7 the branch! andearth Whereas the bell H of the subscriber B is connected between thebranch 2 and earth. In other respects the connection of the apparatuscorresponds to that shown in Figure 2, except that in Figure 3 theconnection of the microtelephone and of the impulse sender to the branch2 is effected through a contact 42 of the switch hook and through acontact controlled by the relay 7. In addition there is included in thecircuit for the relay 1, similarly as in Figure 5, a rectifier 2?. Inthe exchange (the right hand part of the figure) are arranged tworepeating coils 44 and 65 the primary windings of which are fed withringing current. One pole of the secondary winding of the repeating coil44 and 45 respectively is connected with the positive and negative polerespectively of a battery. During the signalling period the linebranches I and 2 are connected with contact springs 46 and 41 of whichcontact spring 46 may be connected alternatively to the negative pole ofthe battery and one pole of the secondary winding of the repeating coil25 respectively. The contact spring 41 may be connected alternatively tothe positive pole of the battery and to the secondary winding of therepeating coil 44 respectively. When ringing up the subscriber 33 havingits bell connected to the branch 2 ringing current is sent through therepeating coil M. The springs then occupy the positions shown in Figure3, the branch I being connected through contacts 43 to the negative poleof the battery and branch 2 through contact 49 and the repeating coil 44to the positive pole of the battery, the ringing current passing onlythrough the bell i! of the subscriber B. The battery is evidentlyconnected to the line and the condensers 3 are in charged condition evenduring the ringing period wherefore the called subscriber can connecthimself to the line also during this period. When ringing up thesubscriber A having his bell 30 connected to the branch I ringingcurrent is sent through the repeating coil 45. The contact springs 46and t? respectively are then shifted in such a manner that the branch Iis connected to the negative pole of the battery through the contact 52and the repeating coil and the branch 2 connected to the negative polethrough the contact 53. The ringing current produced in the transformer45 then passes only through the bell of the subscriber A.

I claim:

1. In a telephone system an exchange, a current source disposed at theexchange and a party line extending therefrom, a number of subscriberstations connected to the said line, a relay and a condenser at eachsubscriber station, the said relay being connected into circuit so as tobe energized by means of discharging current from the condenser chargedby means of the current source at the exchange, and an armature on thesaid relay provided with means to lock the relay in attracted position.

2. In a telephone system an exchange, a current source disposed at theexchange and a party line extending therefrom, a number of subscriberstations connected to the said line, a relay and a condenser at eachsubscriber station, the said relay being connected into circuit so as tobe energized by means of discharging current from the condenser chargedby means of the current source at the exchange, an armature on the saidrelay provided with means to lock the relay in attracted position, afurther relay at each of the subscriber stations, an energizing circuitfor the condenser at each subscriber station, the said 10 relay beingconnected into circuit so as to be energized by means of dischargingcurrent from the condenser charged by means of the current source at theexchange, an armature on the said relay provided with means to lock therelay in attracted 1 5 position, a switch hook at each subscribersstation and means to enable the said switch hook to cooperate with thesaid armature so as to release the armature upon the microtelephonebeing replaced on the switch hook. 20

4. In a telephone system an exchange, a current source disposed at theexchange and a party line extending therefrom, a number of subscriberstations connected to the said line, a relay and a condenser at eachsubscriber station, the said 25 relay being connected into circuit so asto be energized by means of discharging current from the condensercharged by means of the current source at the exchange, another relay atthe exchange adapted to operate in response to a call 30 first comingin, and means controlled by the last mentioned relay to bring about alowering of the voltage impressed upon the line when the line is free.

5. In a telephone system an exchange, a cur- 35 rent source disposed atthe exchange and a party line extending therefrom, a number ofsubscriber stations connected to the said line, a polarized relay and acondenser at each subscriber station, the said relay being connected 40into circuit so as to be energized by means of discharging current fromthe condenser charged by means of the current source at the exchange,another relay at the exchange adapted to operate in response to a callfirst coming in, and means controlled by the last mentioned relay toreverse the poles of the charging battery.

6. In a telephone system an exchange, a current source disposed at theexchange and a party line extending therefrom, a number of subscriberstations connected to the said line, a relay and a condenser at eachsubscriber station, the said relay being connected into circuit so as tobe energized by means of discharging current from the condenser chargedby means of the current source at the exchange, a rectifier connected inseries with the said relay, another relay at the exchange adapted tooperate in response to a call first coming in, and means controlled bythe last mentioned relay to reverse the poles of the charging battery.

7. In a telephone system an exchange, a current source disposed at theexchange and a party line extending therefrom, a number of subscriberstations connected to the said line, a relay and 6 a condenser at eachsubscriber station, the said relay being connected into circuit so as tobe energized by means of discharging current from the condenser chargedby means of the current source at the exchange, a switch hook, atresistance connected in series with the condenser when the said switchhook is depressed, the said resistance being so dimensioned that thecharge of the condenser is not essentially influenced by signallingalternating current sent out on the line.

'8. In a telephone system, an exchange; a direct current'source disposedat the exchange and a party line extending therefrom, a number ofsubscriber stations connected to the said line, a relay and a condenserat each subscriber station, the

' said relay having for purpose to connect the said station to the saidline and being connected into circuit so as to be energized by means ofdischarging current from the condenser said condenser being connectedinto circuit so as to be normally charged by means of the said source atthe exchange and ready for being discharged through the correspondingrelay immediately upon the calling of the subscriber.

9. In a telephone system, an exchange, a direct current source disposedat the exchange and a party line extending therefrom, a number ofsubscriber stations connected to the said line, a relay and a feedcurrent blocking condenser at each subscriber station, the said relayhaving for purpose to connect the said station to the said line andbeing connected into circuit so as to be energized by means ofdischarging current from the condenser said condenser being connectedinto circuit so as to be normally charged by means of the said source atthe exchange and ready for being discharged through the correspondingrelay immediately upon the calling of the subscriber.

DOUGLAS CORMACK CROWE.

